The present invention relates generally to insect control and more particularly to insect control articles that are effective in killing or repelling mosquitoes within the air of a room or the volume of air in the vicinity of a person sitting on a patio, at a picnic table, or the like.
For certain applications, it is important to be able to control flying insects for six to ten hour or even longer periods within defined spaces such as the enclosed space of a bedroom. That duration of insect control is desirable, for example, to protect a sleeper occupying an unscreened room from mosquitoes for a single night. It is also useful to be able to deliver an insect controlling amount of active ingredient nightly for multiple nights in succession. Successful flying insect control is also useful in other living spaces, including even screened areas that for any reason are still subject to invasion by flying insects, as well as outdoor areas such as a patio, a picnic table, or the like.
Traditionally, articles or devices that dispense insecticide vapors to control such insects in such settings require heating or burning a liquid or solid substrate to evaporate the active ingredients. For example, conventional citronella candles have long been used for such purposes. Burning insect coils are also commonly used to achieve a night""s insect control or to control mosquitoes or other insects for an outdoor party or picnic. The product sold by S. C. Johnson and Son, Inc. of Racine, Wis. under the mark xe2x80x9c45 Nights(copyright)xe2x80x9d is an example of a type of product known in the art for delivering insect control over repeated periods of use, such as a nightly use in an unscreened bedroom. The 45 Nights(copyright) product is an example of conventional heated, liquid evaporation insect control products.
The products referred to above all can be effective, within certain limits. However, products that require a heat source also require a safe burning site, in the case of insect coils, for example, and a safe location and source of house electrical current for typical heated evaporation products. Products exist that are designed to avoid some of these difficulties by employing passive evaporation of insect control active ingredients without the application of heat. However, they have problems and limitations of usefulness when compared to products and insect control strategies employing the application of heat.
For example, Regan, U.S. Pat. No. 339,810 uses a tobacco preparation as a repellent that is first soaked into cloth or paper and then dried. The repellent active ingredient is reported to evaporate from the substrate to repel insects. More recent technology has included the use of pyrethrum or pyrethroid materials as passively evaporated insect control active ingredients. For example, see Landsman, U.S. Pat. No. 3,295,246. Ensing, U.S. Pat. No. 4,178,384 employs pyrethroids as repellents applied to the locus to be protected.
Whitcomb, U.S. Pat. No. 4,130,450 describes an insecticide-impregnated, open, low-density web that provides an expanded surface that may be loaded with contact insecticides, including pyrethrum and synthetically prepared insecticides. Whitcomb prefers the use of micro-encapsulated pyrethrum to avoid pyrethrum instability when exposed to ultraviolet light and oxygen. Whitcomb mentions that the web may be hung to permit vaporization of the active ingredient to combat flies. Similarly, Chadwick et al., U.S. Pat. No. 5,229,122 utilizes a mixture of micro-encapsulated and non-micro-encapsulated active ingredients, noting that any known pesticide may be used for the purpose. Pyrethrum or a pyrethroid equivalent are referred to as possible pesticides. The preparation is used to coat surfaces, although it is also noted that the vapor phase of the pesticides may be valuable.
Kauth et al., U.S. Pat. No. 4,796,381, is an example of the use of paper or textile strips impregnated with insecticide that is allowed to evaporate to control insect pests. The Kauth et al. materials utilize pyrethroids and, in particular, vaporthrin, permethrin, and bioallethrin. However, the devices of Kauth et al. are designed to be hung in closets or placed in drawers, suggesting that they are understood to be inadequate to protect larger, more open spaces. Nothing in Kauth et al. suggests any ability of their paper or textile strips to control insects in relatively large air volumes when held within a moving air stream.
Samson et al., U.S. Pat. Nos. 5,198,287 and 5,252,387 disclose a fabric for use in a tent, the fabric including a coating that contains evaporatable insecticides, and in particular, permethrin. Again, a confined space is being protected.
Aki et al., U.S. Pat. No. 4,966,796, utilizes a pyrethroid insecticide on kraft paper, with additional layers of untreated kraft paper added to create a material useful for making an insect-resistive packaging material or bag.
Landsman teaches the use of an insecticide-soaked and then dried paper that is coated with resin to slow evaporation of the active ingredient. The resin coating is deemed important to make an insecticide product that will be effective over a usefully long period of time. Example formulations cited in Landsman include pyrethrins as active ingredients. The Landsman product is not intended to protect large volumes of air and is also an example of the difficulty known in the art of achieving protection over an extended period of time because of the evaporative rate of active ingredients.
Ronning et al., U.S. Pat. No. 4,765,982 is an example of the use of micro-encapsulated active ingredients to achieve a sustained release insect control effect. Pyrethroids, either synthetic or xe2x80x9cnatural,xe2x80x9d are cited as useful. The Ronning et al. insecticidal device may be hung in the open to achieve a repellent effect in a restricted locale to drive insects from a nest or the like.
Yano et al., U.S. Pat. No. 5,091,183 and Matthewson, U.S. Pat. Nos. 4,940,729 and 5,290,774 cite specific insecticidal compounds for volatilization. Yano et al. specifically discusses the use of impregnated papers for heatless evaporation of an insecticidal compound.
Clarke, U.S. Pat. No. 2,720,013, describes the use of a fabric material into which active ingredients are pressed or fused. Pyrethrum is cited as useful not by itself but as at least one element in a mixture of insecticides. The Clarke fabric material is designed to be adhered to the blades of an electric fan so that the insecticide will be directed into the area ventilated by the fan.
In overview, although passive evaporation of insecticides, including pyrethroids, is known in the art, the nature of those materials has been such that the attention of the art generally has been directed to their application to closely restricted spaces or to the area in the immediate vicinity of the materials. Within that context, the art has focused on the need to provide for artificially extending the longevity of insect control by use of a slow release structure or regimen of some sort, or the like. Heat and not passive evaporation has been the predominant means to achieve practical distribution of insecticide throughout a large volume of air, and heated evaporation from a liquid reservoir has been the practical means of achieving protection over a multiplicity of days.
The insect control article of the invention to control flying insects is summarized in that a substrate is impregnated with an active insect control ingredient that is available for passive evaporation. The active insect control ingredient is selected from the group consisting of transfluthrin, prallethrin, 0tefluthrin, esbiothrin, and combinations thereof. Preferably, the active insect control ingredient includes at least one of transfluthrin and tefluthrin, and most preferably the active control ingredient includes at least transfluthrin.
The method of the invention for controlling flying insects is summarized in that it includes the initial step of providing an insect control article having a substrate that is impregnated with an active insect control ingredient available for passive evaporation, wherein the active insect control ingredient is selected from the group consisting of transfluthrin, prallethrin, vaporthrin, tefluthrin, esbiothrin, DDVP, and combinations thereof. Preferably, the active insect control ingredient includes at least one of transfluthrin and tefluthrin, and most preferably the active control ingredient includes at least transfluthrin. The insect control article is then placed in an environment with air movement in such a manner that the substrate of the insect control article is exposed to the air movement. The active insect control ingredient impregnated within the substrate then is allowed to evaporate passively into the air.
As used in this specification, xe2x80x9cinsect controlxe2x80x9d of flying insects is defined as at least repelling and preferably rendering the flying insects moribund. xe2x80x9cPassive evaporationxe2x80x9d is the process by which an active insect control ingredient evaporates from a substrate into the atmosphere through molecular separation, without the application of thermal energy to the substrate, whether by burning the substrate, use of a heating element, or other means. xe2x80x9cMolecular separationxe2x80x9d shall be deemed achieved if particles of an active insect control ingredient cannot be detected by conventional light scattering counter techniques using an instrument such as the Climet Model CI-7300 Light Scattering Counter, made by Climet Instruments Company of Redlands, Calif. This instrument is capable of detecting airborne particles as small as 0.3 microns. xe2x80x9cEffective amountxe2x80x9d shall mean an amount sufficient to attain the desired purpose. A substrate shall be deemed to be xe2x80x9cimpregnatedxe2x80x9d with an active insect control ingredient if that ingredient is generally distributed within or on the material of the substrate in such a manner that the ingredient is directly held within or on the substrate and is supported thereby. An ingredient held within or borne by intervening carriers or delayed-release means such as microcapsules, particles primarily composed of materials other than the ingredient, plastic materials, or the like that are then distributed within a substrate shall not be considered to be xe2x80x9cdirectlyxe2x80x9d held within or on the substrate. xe2x80x9cPorousxe2x80x9d and related terms shall be understood to describe not only materials literally having pores but also, without restriction, loose or open materials and other materials that are fibrous, reticulate, matted, or woven and through or into which fluids may pass.
The insect control article to control flying insects of the present invention falls within the class of insect control articles that include a substrate impregnated with an effective amount of an active insect control ingredient available for passive evaporation from the substrate. The substrate of the invention may be made of any material capable first of receiving and holding an active insect control ingredient and then of releasing it by passive evaporation. Suitable materials include, without limitation, paper-board, open pore cellulosic materials, coiled corrugated paper, woven cloth and non-woven pads or felts of any suitable fiber, gels, absorbent solid-porous foams such as a reticulated, open cell polyurethane foam, and finely divided, channeled, or honeycombed structures molded of non-porous plastics. Depending on the context within which the insect control article of the invention is to be used, either coiled corrugated paper or a piece of flat, open-surfaced paper presently is preferred, although the use of the molded plastic structures referred to has advantages of manufacturing convenience.
As is noted in the discussion of Background Art, above, the art teaches the use of various insecticides for passive evaporation for the control of insects, for the most part although not exclusively in drawers, closets, tents, and other very limited spaces or as insecticidal barriers intended to affect insects in close proximity to a treated carrier strip or the like. This teaching of the art would lead one to expect equally successful flying insect control from the passive evaporation of pyrethrum, sometimes microencapsulated (e.g. Landsman, Clarke, Whitcomb, Chadwick et al.), pyrethroids in general (e.g. generic references in Ensing, Ronning, et al., and elsewhere), and particular pyrethroids, such as permethrin (Samson et al., U.S. Pat. No. 5,189,287), vaporthrin, permethrin, bioresmethrin, bioallethrin, kadethrin, decis, cyfluthrin, and fenfluthrin (Kauth et al.) and permethrin, deltamethrin, cyhalothrin, and cypermethrin (Chadwick et al.). These examples are intended to be illustrative and not exhaustive.
To the limited extent that the art is suggestive or predictive of success, all of these insecticides would appear equally attractive, along with apparently equally attractive non-pyrethroid insecticides (Whitcomb, Clarke, etc.). However, in research discussed below, the present inventors have found that in fact, with the possible exception of vaporthrin and dichlovos (DDVP), the examples of these materials that were tested were not sufficiently effective to be employed successfully for the practical control of mosquitoes, for example, in a space as large as a typical sleeping room or in the open area surrounding a picnic table or patio.
xe2x80x9cPractical controlxe2x80x9d shall be understood to require, at the minimum, the ability of a substantially planar substrate, such as a flat paper or cloth, not larger than about 645 cm2 (100 in2) to achieve at least 50% repellency of mosquitoes within a volume of air not less than 27 m3 within 20 minutes when that substrate is impregnated with not more than a gram of insect control active ingredient and when the substrate is suspended directly in the airflow of a common 51 cm (20 inch) house fan, in accordance with the fan chamber test protocol, described below. This shall be referred to herein as the xe2x80x9cminimum practical control standard.xe2x80x9d
Preferred is the level of practical control demonstrated by the ability of a standard high air-transmitting substrate, described below, impregnated with not more than 1 gram of insect control active ingredient to achieve that same repellency effect within 30 minutes when subjected to an airflow through the substrate of not more than 0.06 m3 per minute. The standard high air-transmitting substrate by which this level of practical control may be determined is a 0.5 cm thick, 4.5 cm diameter coil of common corrugated cardboard, with the channels of the corrugation presented endwardly to the direction of air flow. This shall be referred to herein as the xe2x80x9cpreferred practical control standard.xe2x80x9d
It has now been discovered that unexpected and favorable results are achieved in the practical control of flying insects when the active insect control ingredient used in the insect control article of the invention is selected from the group consisting of the pyrethroids transfluthrin, prallethrin, vaporthrin, tefluthrin, and esbiothrin, or the non-pyrethroid DDVP and combinations thereof. To most easily achieve the minimum practical control standard and especially when the preferred practical control standard is to be achieved, it is preferred that the active insect control ingredient include at least one of transfluthrin and tefluthrin. Of those two, transfluthrin is preferred as less irritating and otherwise objectionable for use in the presence of humans.
The particular active insect control ingredients disclosed now have been found to be sufficiently effective as insect control active ingredients that their airborne concentration is sufficient to achieve control of flying insects and, in particular, of mosquitoes and flies, when these ingredients are delivered by passive evaporation into the air when the substrate of the invention is placed in an environment with air movement at air temperatures between 10xc2x0 C. and 45xc2x0 C. At the same time, these selected materials"" vapor pressures at those temperatures are low enough that it is practical and economical to use them as active ingredients on substrates of a convenient size in amounts sufficient to achieve such insect controlling concentrations over time periods long enough to be sufficient to protect a room overnight or even for a series of nights. A useful commercial goal is to achieve protection for at least thirty consecutive nights of use. By use of the active ingredients of the invention, this goal is within practical reach.
Any effective conventional method may be used to impregnate the substrate with the active insect control ingredient. Typically, the substrate is impregnated with the active insect control ingredient by dissolving an appropriate amount of the active insect control ingredient in a solvent, thoroughly wetting the substrate with the solvent, and then drying the substrate to evaporate the solvent contained in the substrate and leave the substrate impregnated with the active insect control ingredient. If air transmission through the substrate is desired, the substrate preferably is not coated or printed with a layer of the active insect control ingredient. This is because the coated or printed surface is likely to inhibit air movement through the substrate, thereby decreasing the rate of passive evaporation of the active insect control ingredient. However, coating or printing a substrate may be effective when air is to merely pass over and not through the substrate.
The amount of active insect control ingredient per square centimeter of substrate necessary to be effective to control flying insects in an insect control article of the invention will depend upon the overall size of the substrate used, the rate of air movement over or through the substrate, and the longevity of effectiveness desired. Preferably, the active insect control ingredient is present approximately in an amount of from 0.1 to 10 milligrams per square centimeter of macro surface area, when conventional, essentially planar substrates such as papers, corrugated cardboard coils, or felts are used. For the purpose of this discussion, xe2x80x9cmacro surface areaxe2x80x9d means the surface area as measured with a ruler or similar device, as opposed to the micro surface area as measured taking into account porosity, surface convolutions, finely divided materials, and the like. A very porous or finely divided substrate may hold additional amounts of active insect control ingredient in a given macro surface area, allowing for use of a smaller macro surface area of substrate. However, the preferred amounts of the active insect control ingredients identified above per square centimeter of macro surface area result in a substrate of a size convenient to handle and otherwise deal with when the material of the substrate is common paper, felted and woven materials, and the like, and when substantial insect control within a typical sleeping room, for example, is to be achieved for at least eight hours by placing the substrate in the air flow generated by conventional electric cooling fans. Disks of paper approximately 15 to 25 cm in diameter or approximately 25 cm square pieces of felted or woven cloth have proved convenient sizes for use with common, free-standing house fans, such as the square, 51 cm (20 inch) box fans conventionally available for household use. However, the invention is not limited to these precise sizes.
The insect control article of the present invention can be placed in any environment where there is air movement that will pass through or over the impregnated substrate, thereby allowing the active insect control ingredient to continuously passively evaporate into the atmosphere for an extended period of time. Suitable environments include enclosed rooms as well as volumes of open air space, such as patios, the area around a picnic table, and the like, with air movement provided by fans, air circulating systems, open windows, or the like.
In one embodiment of the present invention, the insect control article includes hanger means for suspending the impregnated substrate in a suitable environment provided with air movement to allow the active insect control ingredient to passively evaporate into the atmosphere. In another embodiment, the article includes attachment means for attaching the impregnated substrate to means for circulating air. Examples of such means for circulating air include but are not limited to conventional room fans. Examples of suitable hanger or attachment means for both embodiments include hooks, strings, mechanical clips and fasteners, adhesives, and the like. Any such means provided on the substrate should not substantially block the passage of air through or over the substrate.
When the impregnated substrate is attached to a fan, the impregnated substrate preferably is attached at a point separated from the fan blades sufficiently to allow the air stream to pass from the blades and then through or over the substrate, thereby facilitating the passive evaporation of the active insect control ingredient from the substrate. Attachment directly to the surface of the fan blades is not deemed satisfactory, because the air stream may not pass sufficiently through or over the substrate to achieve adequate insect control, an effect demonstrated in the Examples, below.
The method of the invention for controlling flying insects includes, as a first step, providing an insect control article to control flying insects that includes a substrate that is impregnated with an active insect control ingredient selected from the group consisting of transfluthrin, prallethrin, vaporthrin, tefluthrin, esbiothrin, DDVP, and combinations thereof. The insect control article is then placed in an environment with air movement, and the substrate of the insect control article is exposed to the moving air. Preferably, the substrate is located at a selected distance from any fan or equivalent means for moving air that is being used to create air movement. The active insect control ingredient with which the substrate is impregnated is then allowed to passively evaporate into the air.